Quantitative analysis of proteins by electrophoresis into antibody containing agarose gel - the electroimmuno assay - is described with special reference to technical details and to the variation in appearance of the immunopreci-pitates in different antigen-antibody systems. The utility of the method is compared with the single radial immunodiffusion technique. Both methods have similar sensitivity and precision. They are simple enough for clinical routine work. The results are obtained faster and differences in size of the antigen-carrying molecules in samples are often easier to recognise with the electrophoretic technique, which also facilitates evaluation of separations obtained on protein chromatography.